Dynamic bias control techniques such as envelope tracking (ET) or envelope elimination and restoration (EER) are applied to the design of a radio frequency (RF) power amplifier to enhance its efficiency. In such case, securing a linearity of the RF power amplifier may become another design concern. For instance, the dynamic bias controlled power amplifier may suffer from a gain distortion in an output RF signal, which needs to be suppressed in order to secure the required linearity. Further, although the gain distortion may be resolved by a specific device or method, it does not guarantee the required linearity unless a phase distortion in the output RF signal is removed or bounded within a specific range.
What is needed, therefore, is an apparatus that overcomes at least the shortcomings of the known RF power amplifier discussed above.